This invention relates to medical devices.
The invention is more particularly concerned with catheters or the like, that are visible under ultrasound observation.
Ultrasound imaging equipment is increasingly being used during surgical procedures to monitor the location of a device within the body. The visibility of a device under ultrasound depends on various factors including the difference between the acoustic impedance of the material of the device and that of the surrounding medium, such as the patient tissue or body fluid within which the device is located. This difference is relatively low with plastic devices such as catheters and may make conventional catheters difficult to locate. Even devices of metal, such as needles, present problems of visibility under ultrasound observation because of the directional nature of the reflections. In some orientations a metal needle may be clearly visible but in other orientations it may be considerably less visible.
Attempts have been made to increase the visibility of medico-surgical devices under ultrasound observation in various ways. The surface of the device may be modified, such as by forming grooves or indentations in its surface. A reflective coating may be applied to the device, such as incorporating bubbles, as described in WO98/19713 and EP0624342. Alternatively, a metal marker may be secured to a plastics catheter. GB2379610 describes a catheter where the wall is made entirely of a plastics including gas bubbles or where bubble-containing material is in a stripe occupying only a part of the circumference. Although this latter form of catheter has various advantages, it has been found that there is a tendency for the surface of the bore through the catheter to be interrupted by small protrusions where the bubbles break the surface. In some applications, such as for embryo transfer, it is important that the bore of the catheter is as smooth as possible so any interruption of this is a disadvantage. In other applications it may be important instead for the outer surface to be as smooth as possible, or for both the outer and inner surface to be smooth.